Method for the production of yeast



Patented June 13, 1939 warren STATES Parent OFFICE WTHOD FOR THEPRODUCTION OF WAS'E Johann Hilbers, Oldenburg-Etzhorn, Germany NoDrawing.

Application January 14, 1937, de-

rial No. 120,512.- In Germany January I, 1936 5 Claims.

vent any infection of the yeast. The addition of acid which prevents thegrowth of undesired cultures does, however, not hinder the developmentof yeast which has a relatively high resistance against acid. For thesereasons in the methods known hitherto, the fermentable liquid is, aftercompletion of the main fermentation, kept weakly acid for which purposesulphuric acid is eventually added. Yeasts produced according to thismethod generally were satisfactory, but often had a small stability andafter a short time of storage show a, decrease in the capacity for'forming a head and a tendency to become gritty.

Now it has been found, that a substantially better maturated yeast ofcorrespondingly greater stability may be obtained if, before completionof the main fermentation which at first, is carried 'out in well knownmanner under weakly acid conditions, the wort is brought to the neutralpoint with regard to litmus paper after addition of all the alkali, andthe fermented wort being neutral is, after finishing the addition 01'the molasses, further aerated until perfect maturation of the yeast isobtained. Any change of the wort over to the alkaline side is positivelyprevented by the fact, that the wort at the end of the main fermentationprocess is brought to the neutral point by continuing the initialpowerful aeration.

It has already been proposed to inhibit, the increase of acidityproduced by the mineral acids liberated by the yeast in order to removethe harmful influence of these mineral acids on the growth of the yeast.The presence of organic acids which do not unfavorably influence thegrowth of the yeast has, however, been considered hitherto asindispensable for the reasons given above.

The assimilating capacity of the yeast cells is increased according tothe new method by means of the continued powerful aeration after theaddition of the wort has been finished. The yeast cells, therefore, atfirst consume the total amount of sugar present and finally also thesmall amounts of organic acids present. Only after the liquid is free ofsugar and acid, does the yeast arrive at a maturated final condition inwhich it has an excellent stability. The yeast maturate's and sodeposits the substances taken up in the cell in a manner required in thecondition of rest.

Substances no longer used by the cells are disposed off and thereforeremoved during the subsequent washing, separating and pressing of theyeast. The wall oi the yeast cells obtained is then clean and does notshow a cover layer which forms a nutritive soil for bacteria which spoilthe yeast and influence the color of the same.

Such a. perfect maturation of the yeast cells is impossible in themethods known hitherto using an acid solution, since the yeast cellstake up the organic acids as nourishment just as they :do the sugar andtherefore they do not perfectly come to rest. A yeast not perfectlymaturated continues to work after pressing. The substances present inthe cell are re arranged and partly separated, whereby the capacity ofthe yeast for forming a head is decreased. With a sticky condition beingpresent in the substance disposed of,

moreover, the feared gritty condition results.

Even if thisphenomenon does not occur, the emudation of nutritioussubstances is harmful to the yeast, because such substances form thenu-' tritive soil for the bacteria-which spoil the yeast.

As according to the new method, the yeast is obtained in a maturatedfinal condition and no exudation of nutritious substances or the likeoccurs after pressing, it is also possible to operand steam are saved,but, moreover, a yeastof greater dryness is obtained. with the sameweight of the wet yeast and equal albumen contents, the purchaserreceives a greater amount of albumen in the dry substance.

To explain the subject matter of the invention, the known and the newmethod are compared below in one example each. In both examples 3500 kg.of molasses are treated according to the additory process under additionoi corresponding amounts of phosphorus and nitrogen. In both methods anyraw materials may be used. Therefore, molasses cleared chemically aswell as by a separator may be employed. Moreover, nitrogen may he addedas ammonium biphosphate,

ammonium persulphate and ammonia, whereby litmus.

2. portionoithe nitrogen istobeintroduced as.

lixnlrtli xnownmethod lncarryingouttheunialmethodfirstoiaii .700 kg.oiyeast are broughttoan acid content.

i 2' and the yeast is lei't to'itseli for an hour. The stated degree oiacidity isthenreached ii 2 cm. oi N caustic soda solution. are requiredto neutralize the same with regard tollitsnus and cm. oi the yeastfloating in the water. Then .25. cm. oi a diluted wort, containing 400kg.oi molasses, are filled into a container or vatoi a capacity of 120in. and mixed with the pitching yeast prepared in the manner statedabove. The wort is now so iar acidified, that 0.5 cm. oi N/ 1,0 causticsoda solution are ior 20 an. oi worttoreachtheneutralpointwithregardtoThe wort at first has a concentration oi 1.55 Bailing. Now the wort isaerated by 3000 m." of air per'hour, thereby starting the iermentation.Aiter a pre-iermentation of a period oi one hour, the addition of theremaining 3100 kg. of molasses is'started. During the supply of molassesextending over a'period of 9.5 hours the iermentation is carried out insuch a manner, that the degreeoi. acidity substantially remainsconstant. The amounts of nitrogen and ammonia required are added in thefirst 8 hours. by 61.5 kg. ammonium biphosphate and 103 liters of aammonia. To stop a decrease of the degree of acidity aiter addition oithe salts, the supply of air is reduced. 2 hours beiore.

finishing the addition oi molasses, reduced to 2400 in. and then to 1500in. per hour.

Aiter finishing the addition oi molasses, the

' vat cmtains as m.' oi a wort of 111' Bailing. The

degree oi accidity content of the wort is after completion of theaddition so great, that about 0.4 cm. of an N710 caustic soda solutionare required to neutralize 20 cm. oi wort with regard to litmus. Aiterexpiration oi one hour, the amount oi caustic soda solution required forthe neutralization oi 20cm. oi wort has dropped to- 0.25 cm. To maintainthe degree of acidity 2 liters oi a. 60% concentrated sulphuric acid areadded and the air supply is gradually cut oil, so thatthe wort is slowlyagitated only.

Ai'ter a total period oi 13 hours oi fermentation the wort, at thebeginning oi the separation, has a concentration of 1.72Bailing. 20 cm.oi wort require 0.3 cm. of an N/l0 caustic soda solution forneutralization with regard to litmus.

The yeast output amounts to 2310 kg. of yeast which after deduction of700 kg. oi pitching yeast corresponds to an output oi 46% with regard tothe molasses used. The percentage of nitrogen of the pressed yeastamounts to 1.83%. with a dry content oi 26.51% an albumen content oi24.52% results.

Exams 2 New method In carrying out the new method 600 kg. of yeast areat first brought to an acid content oi 2 and then the yeast is leit toitseli for 1 hour. Then m. of water are filled into a container or vatof a capacity oi m. and mixed with they pitching yeast prepared in themanner stated above. The wort has a concentration oi l.0 Bailing and 20cm. of the wort require 0.35 cm of an N/ 10 caustic soda solution forneutralization with regard to litmus. The wort at first iree oi molassesis now aerated by supplying 3000 m. oi air-per hour and is then mixedgradually during a period oi 1 1 hours with 3500 kg. oi molasses. Duringthe iermentation thereby taking place, the concentration stated inBailing is gradually increased, because irom the beginning or vat isfilled with the total amount "oi water required. The degree oi acidityis kept as low as possible. A certain acidity is required to absolutelyprevent turning oi. the wort over to the alkaline side during-theaddition. oi nitrogen and'phosphorus in the first 9 hours. The nitrogenand phosphorus are supplied in the form oi 150 kg. of superphosphate,45kg. oi ammonium per-sulphate and 85 liters oi ammonia of 25%. Aiteraddition of the total amounts oi nitrogen and phosphorus, i. c. afterthe iermentation oi 9 hours, 0.4 cm. oi an N/10 caustic soda solutionare required to neutralize 20 cm. of wort with regard to litmus. Byuniiorm'maintenance or a strong aeration the acidity drops, so thataiter IO'h'oursonIy 0.25 cm. oi an'N/ 10 caustic soda solution arerequired ior the neutralization of the same amount oi wort and after theaddition oi the molasses is finished, i. c. after 11 hours, the wort isneutral with regard to litmus. The aeration with 3000 m3 oi air per houris, aiter reaching the neutral point, continued for a short period oftime to prevent any re-iormation of acid. Theaeration is then graduallyreduced and interrupted aiter iurther 2% hours. The yeast is nowperiectly maturated in the wort free oi sugar and acid.

An amount oi wort oi 42 m.',is obtained with a concentration of 3.4Bailing. The yeast output amounts to 2481 kg. which after deduction of600 kg. oi the pitching yeast corresponds to an output-oi 53.74% withregard to the molasses. The alcohol output which also results amounts to320 liters=12% also. related to molasses.

The nitrogen content oi the pressed yeast amounts to 2.33% which with adry content of 32.06% corresponds toan albumen content oi oi course, theinvention is not to be limited to the statements given in the aboveexamples, since alterations in many respects may be made in accordancewith the operating conditions.

Having now fully described my invention, I claim? :3

1. A process iormanuiacturing yeast by propagation with aeration, whichconsists in suspending seed yeast in an aqueous liquid oi weak acidity,subjecting the weakly acid aqueous liquid to aeration and addingcontinuously molasses and other yeast nutrients, stopping the additionof the yeast nutrients when a suiilcient amount thereof has been addedto produce the predetermined amount oi yeast, neutralizing the resultingwort by aeration and continuing the aeration until perfect maturation oithe yeast is obtained.

2..A process for manufacturing yeast by propagation with aeration, whichconsists in suspending seed yeast in an aqueous liquid oi weak acidity,subjecting the weakly acid aqueous liquid to powerful aeration andadding continuously molasses and other yeast nutrients, stopping theaddition oi the yeast nutrients when a sufllcient amount thereof hasbeen added to produce the predetermined amount oi yeast, neutralizingthe wort by continuing the initial poweriul aeration, and furtheraerating the resulting neutralized wort until perfect maturation oi theyeast is ob tained.

3. A process ior manufacturing yeast by propagation with aeration, whichconsists in suspending seed yeast in an aqueous liquid of weak acidity,subjecting the weakly acid liquid to areation and adding continuouslymolasses and other yeast nutrients in suflicient quantities to produce awort of high concentration, stopping the addition of the yeast nutrientswhen a sufficient amount thereof has been added to produce thepredetermined amount of yeast, neutralizing the concentrated wort byaeration thereof, and continuing the aeration of the resultingneutralized wort until perfect maturation of the yeast is obtained.

4. A process for manufacturing yeast by propagation with aeration, whichconsists in suspending seed yeast in an aqueous liquid of weak acidity,subjecting the weakly acid aqueous liquid to powerful aeration andadding continuously molasses and other yeast nutrients in suflicientquantities to produce a wort of high concentration, stopping theaddition of the yeast nutrients when a suflicient amount thereof hasbeen added to produce the predetermined amount of yeast, neutralizingthe concentrated wort by continuing the initial powerful aeration, andfurther aerating the resulting neutralized wort until perfect maturationof the yeast is obtained.

5. A process for manufacturing yeast by propagation with aeration, whichconsists in suspending seed yeast in an aqueous liquid of weak acidity,subjecting the weakly acid aqueous liquid to powerful aeration andadding continuously molasses and other yeast nutrients includingnitrogen and phosphorus in suflicient quantities to produce a wort ofhigh concentration, stopping the addition of the molasses and also ofthe other yeast nutrients including the nitrogen and phosphorus when asufllcient amount thereof has been added to produce the predeterminedamount of yeast, neutralizing the concentrated wort exclusively bycontinuing the initial powerful aeration, and further aerating theresulting neutralized wort until perfect maturation of the yeast isobtained.

, JOHANN HILBERS.

